Electromagnetic suspension and/or guide system especially for magnetically suspended vehicles

ABSTRACT

An electromagnetic suspension and guide system for magnetically suspended vehicles comprises a support or track along which the vehicle is displaceable and is provided with an armature rail of magnetically permeable material (e.g., a ferrous metal), while the vehicle is provided with at least one electromagnet cooperating with this armature rail. The electromagnet has a core of U-profile, the arms or shanks of which reach toward the armature rail which is likewise of U-profile whose shanks reach toward the electromagnet. The shanks of these two members overlap and the shanks of one member are inclined toward the shanks of the other. The shanks of the armature member may reach into the space between the shanks of the core member or vice versa.

United States Patent 1 Schwiirzler et al.

ELECTROMAGNETIC SUSPENSION AND/OR GUIDE SYSTEM ESPECIALLY FOR MAGNETICALLY SUSPENDED VEHICLES Inventors: Peter Schwiirzler, Furstenfeldbruck;

Gerhard Bohn; I-Ielmut Schauberger, both of Munich, all of Germany Krauss-Maffei AG, Munich Germany Filed: Aug. 11, 1972 Appl. No.2 280,073

Assignee:

Foreign Application Priority Data Sept. 7, 1971 Germany..., P 21 46 143.8

US. Cl. 104/148 MS Int. Cl B6lb 13/08 Field of Search 104/148 MS, 148 SS,

References Cited UNITED STATES PATENTS 4/1973 Karch 104/148 MS 2/1969 Steingroever... 4/1968 Smith 335/299 1 Dec. 25, 1973 1,126,608 l/l915 Woodruff 104/148 LM FOREIGN PATENTS OR APPLICATIONS 1,035,764 7/1966 Great Britain 104/148 MS 707,032 3/1941 Germany 104/148 MS 643,316 8/1934 Germany 104/148 MS Primary Examiner-Duane A. Reger Assistant ExaminerGalen L. Barefoot Attorney-Karl E. Ross [57] ABSTRACT An electromagnetic suspension and guide system for a tisel x ssspea sixehislss semi-21 2s esq or track along which the vehicle is displaceable and is provided with an armature rail of magnetically permeable material (e.g., a ferrous metal), while the vehicle is provided with at least one electromagnet'cooperating with this armature rail. The electromagnet has a core of U-profile, the arms or shanks of which reach toward eazmatu e rai s hichisfihawiss of -P whose shanks reach toward the electromagnet. The shags oilthese twornembers overlap and the shanks of one member are in c lined toward the shanks of the other. The shanks o f the armature nernhermav reach into the s p ace between the shanks of the core member of vice versa.

10 Claims, 10 Drawing Figures PATENIEU 2 I 3,780,668

I SHE 1 BF 5 Fig. 2

PATENTEB UEC25 I975 SHEET 3.- OF 5 Fig. 5

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PATENTED B5325 3, 780 668 sum u nr 5 PATENTEU UEE 2 51975 SHEUSBFS I FIG. /0

FIG. 9

ELECTROMAGNETIC SUSPENSION AND/OR GUIDE SYSTEM ESPECIALLY FOR MAGNETICALLY SUSPENDED VEHICLES FIELD OF THE INVENTION The present invention relates to magnetic suspension and guide systems and, more particularly, to an electromagnetic suspension or guide system for magnetically suspended vehicles.

BACKGROUND OF THE INVENTION In recent years considerable effort has been expended in attempts to devise mass transportation and high-speed transportation systems without the disadvantages of conventional arrangements. For the most part, any transportation system of this type must comprise a track or support which is located above grade, at grade level or below grade, and a vehicle displaceable along this track. One of the principal disadvantages of conventional vehicular systems of this type is the friction between the vehicle and the track.

More recent developments have made use of air cushion tenchiques for suspending the vehicle or supporting the vehicle upon the track, this system having the disadvantage that displacement of air in large volumes is required to maintain a stable air cushion in the gap between the vehicle and track. The displacement of air in this manner is noisy, requires bulky equipment and is not desirable in many urban centers.

The displacement of vehicles along a track may make use of fluid-pressure differentials, linear-induction motors and other non-contact or limited contact motive systems, i.e., systems in which frictional contact between the vehicle and track is minimized. However, unless the supporting and guiding functions are also frictionless or of limited friction, the practical vehicle speed remains limited.

The present applicants and others have disclosed heretofore magnetic suspension systems whereby the disadvantages of some of the earlier vehicle-support and vehicle-guide arrangements can be overcome. In general, a magnetic suspension and guide system may include one or more armature rails extending along the track and one or more electromagnets cam'edby the vehicle and having cores cooperating with the armature rails of the track or support to maintain an air gap therewith across which magnetic force supports the vehicle. A magnetic-flux path is closed between the poles of the electromagnet core through the armature and across the gap.

In prior-art magnetic suspension systems, especially for magnetically suspended vehicles, the armature was a flat bar and the system was characterized by an unstable force characteristic. When the system was used as a suspension arrangement, therefore, the vehicle could be laterally and longitudinally dislocated or shifted by such forces as wind, centrifugal force as the vehicle passes around a curve etc., without significant controllability. When the system was used for guiding purposes, some freedom of movement is provided in the parallel power to the plane of the air gap and hence an unstable condition is created in this situation as well. In order to avoid this instability with two degrees of freedom, electronic control was necessary for each degree of uncontrolled movement. In other words, electromagnets were provided to adjust both lateral and vertical air gaps and to limit the displacement of the vehicle in the vertical and lateral directions, and even to stabilize the vehicle against displacement in a longitudinal mode. For each electromagnet system a separate gap detector and feedback circuit was provided to regulate the energization current through the respective coil to maintain the gap at desired level.

As a result, the electronic control system for conventional,.magnetic suspensions having two or more degrees of freedom or instability was highlycomplex, expensive and massive, thereby decreasing the carrying capacity of the vehicle and increasing the operating and capital cost.

OBJECTS OF THE INVENTION It is the principal object of the present invention to provide a magnetic suspension and guide system, preferably for the contactless support and/or guidance of a vehicle whereby the control-system costs can be held relatively low.

- It is another object of the invention to provide an improved magnetic suspension and guide system whereby the aforedescribed disadvantages can be obviated.

Still another object of the invention is to provide a magnetic suspension and guide system for a magnetically suspended vehicle in which fewer gap-responsive control circuits are necessary to limit instability.

SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, which comprises an electromagnetic suspension and/or guide system, especially for magnetically suspended vehicles adapted to travel along a support track, which comprises at least one armature rail extending along this track and having a web from which a pair of shanks reach toward a portion of the vehicle, and at least one electromagnet whose coil member is of U-profile with a pair of shanks reaching toward the armature member, the shanks of one of these members being inclined toward the shanks of the other member and overlapping the same. A coil is wound upon this core.

More specifically, the armature member is constituted substantially of a U-cross-section channel whose lateral shanks or arms are spaced from and overlapping with the lateral shanks or arms of the U-cross-section electromagnet core whereby the shanks of one of these members is received between the shanks of the other member. The shanks of one of the members, moreover, are inclined toward the shanks of the other member so that the region of overlap has a location of closest approach at which the inclined shanks are closest to a flank of the noninclined shank or the shank with which they overlap proximally of the web and divergent from this shank in the direction of its free end. Between each inclined shank and the noninclined shank of the other member, therefore, a wedge-shaped air gap is provided.

A system of this typedevelops an attractive force in the direction of the longitudinal axis in which the center of gravity of the cross-sections or profiles (centroids) lie and which maintains stability along this longitudinal axis over a limited range of positions of the electromagnet.

This system is defined as a system having longitudinal stability, i.e., without change in theelectrical current traversing the electromagnet, the magnetic force resisting displacement along the longitudinal axis increased with displacement to provide a so-called force characteristic which has a spring constant similar to the force characteristic of an extension spring which is deformed.

The increasing magnetic attraction with separation of the interfitting core member and rail member results from the fact that the magnetic flux bridging the air gap between the two shanks of each overlapping pair is a stray flux which is unconcentrated over the full length of the shank. As the degree of overlap is reduced, the stray flux is reduced and the flux density at the reduced regions of juxtaposition (poles) increases.

The force characteristic reaches its maximum when overlapping practically ceases, i.e., at the point at which the free end of the arms of the yoke or core of the electromagnet and the free ends of the arms of the armature rail lie in a common plane perpendicular to the longitudinal axis defined by the centroids. At this point of total separation, increased adhesive force with increasing displacement no longer develops and the magnetic suspension is no longer stable even in one direction. With overlapping of the shanks and interfitting of the two channel-shaped members, the system is transversely unstable, this degree of instability remaining when the two components of the system are separated. The transverse instability is seen in the fact that a displacement of the core member relative to the rail member in a direction perpendicular to the plane of the longitudinal axis defined by the centroids of the profile sections, is not magnetically resisted by the flux traversing the core and rail members.

It is, therefore, a feature of the present invention to providea further electromagnetic system, preferably including a magnetic armature rail and electromagnet, which is effective in the transverse direction for limiting such displacement. The further electromagnetic system may be provided with a gap sensor or detector for adjusting the electromagnetic force to compensate for or resist the transverse forces. It should be understood that an arrangement of this type uses control circuitry only for one degree of possible vehicle displacement, since any tendency for the vehicle to shift with the other degree of freedom is counteracted automatically because of the inclined orientation of the shanks of the armature or core. In practice, it has been found that the control circuitry need only respond to minor vehicle displacements, e.g., to damp vehicle oscillation.

Another advantage of the present system resides in the relatively large freedom of movement of the magnetically suspended system in the longitudinal direction by comparison with systems using flat armatures. The system of the present invention can thus provide tracks, rails and like structures which interact with mating facilities of the vehicle with larger tolerances than is possible with the prior art arrangements.

The electromagnet of the present invention may be made relatively wide with relatively short lateral shanks or arms such that the lateral shanks or arms of the armature can be received between the shanks or arms of the electromagnet core. A system of this type is characterized by reduced stray flux between the relatively widely spread lateral shanks of the magnet core, by the ability to use wide electromagnet coils and hence by reduced coil-winding height.

When the system of the present invention provides lateral shanks or arms of the armature which embrace the arms of the electromagnet, the active surfaces of the armature and the magnet core is protected from ice, contaminants and the like in a particularly convenient manner.

It has been found, moreover, that it is possible to vary the spring constant and the force characteristic of the system by imparting a curvature to the inclined shank or arm, e.g., by curving the latter more rapidly away from the non-inclined shank or curving it toward the latter. When the system is used for suspension, a stiffer or softer spring characteristic can be provided with increasing load.

It has been found to be advantageous, moreover, to provide the longitudinally stable suspension or guide system for stretches which are relatively stiff and hilly as a suspension system, but as the guide system where the vehicle is expected to travel around large numbers of relatively sharp curves. These preferences are a consequence of the high degree of longitudinal adjustability afforded by the system of the present invention.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a vertical cross-sectional view through a portion of a suspension system embodying the invention, the means for attaching the components to the respective supporting structure being illustrated diagrammatically;

FIG. 2 is a view similar to FIG. 1 of a suspension and guide system representing a variation of the system of FIG. 1;

FIG. 3 (sheet 2 of the drawing) is a view similar to FIGS. 1 and 2 but illustrating a kinematic reversal of the components in a suspension or guide system according to the invention;

FIG. 4 is a view similar to FIG. 3 of still another embodiment of the invention;

FIG. 5 (sheet 1 of the drawing) is a further diagrammatic cross-sectional view, taken in a plane perpendicular to the direction of movement of a vehicle provided with the suspension or guide system and illustrating another aspect of invention;

FIG. 6 (sheet 1 of the drawing) is a view similar to FIG. 5 showing another modification;

FIG. 7 (sheet 3 of the drawing) is a vertical crosssection through a suspension system for a magnetically suspended vehicle in which the longitudinal stability is provided in the suspension portion of the system;

FIG. 8 is a view similar to FIG. 7 of an embodiment of the invention wherein the longitudinally stable electromagnetic system is provided for guiding the vehicle;

FIG. 9 is a side elevational view of one of the electro magnets in accordance with the invention; and

F IG. 10 is a diagrammatic perspective view of a vehicle system embodying the invention.

SPECIFIC DESCRIPTION Referring first to the overall view of a vehicle system according to the present invention shown in FIG. 10, it can be seen that the system may comprise a substantially horizontal support track 50 held at intervals by pylons 51 or other suppor means at grade level, above grade or below grade. The track 50 is provided with a channel 52 which is upwardly open and is overhung by a pair of inwardly turned flanges 53 and 54.

As will be described in greater detail in connection with FIGS. 7 and 8, the undersides of the flanges 53 and 54 are provided with respective downwardly open channels 55, 56 constituting armature rails composed of a ferromagnetic material, e.g., iron, and extending the full length of the track. When, as described below, longitudinal stability of the suspension portion of the system is desired, the rails may have the configuration of any of the rails 1 of FIGS. 1 through 7. However, when guide stability is required, the rail configuration may be that of FIG. 8.

The inwardlyturned faces of the flanges 53 and 54 are also provided with inwardly open rafls 57 and 58 of U-section as also will be described in greater detail in connection with FIGS. 1 through 8.

The vehicle 60 may comprise an operator compartment 61 and a passenger compartment 63 to which axis is had through a door 63. The vehicle may be propelled by a linear induction motor and it receives electrical power through brushes provided on the vehicle and contact rails provided on the support tract 50 in accordance with conventional practices.

The vehicle is provided with a horizontal flange 64 which extends into the channel 52 and carries on its outer edges the electromagnets 65 and 66 cooperating with rails 55 and 56 for suspension of the vehicle. Outwardly facing electromagnets 67 and- 68 are also provided upon the vehicle to cooperate with the armature rails 67 and 68 in guiding the vehicle.

The vehicle is magnetically suspended from the downwardly open U-section rails 55 and 56 and is guided against lateral movement by the electromagnetic forces generated at rails 57 and 58. The result is a frictionless magnetic suspension and guide system.

In FIG. I, the electromagnetic suspension or guide system is shown in greater detail and the principles of operation will become more fully apparent.

Thus, the electromagnetic suspension or guide system, which may be used for the suspension or guide arrangement of FIG. 10, can comprise a fixed armature mounted an electromagnet 5 whose elongated core 6 has a U-shaped profile and carries a coil 8 wound about the web 7.

The arms or lateral shanks 12 of the core 6 reach upwardly to bracket the arms 2 of the rail 1 between them, i.e., the armature rail 1 and the core 6 overlap or interfit with the arms 1 received with the channel or between the arms of the other.

When the coil 8 is electrically energized, a magnetic flux 9 (shown in broken lines) is induced in the core 6, the flux path closing through the air gap between the arms 12 of the core 6 and the arms 2 of the rail 1 and through the latter.

The magnetic attractive force at the gaps, produced by the field 9, and the lateral guide force represented at (see also FIGS. 7 and 8) produced by some other means, e.g., another electromagnet and rail arrangement, maintains the vehicle in the position illustrated in FIG. 1 relative to the rail, thereby freely suspending the supported or guided system represented at 11.

As already noted, the lateral flanges, arms or shanks 2 and 12 of the armature rail 1 and the core 6 overlap in this position and define gaps between them which diverge in the direction of the support structure. Of

course, it is not critical to the present invention that the direction of divergence be toward the support structure it being only significant that the direction of convergence be such that a tendency toward separation will reduce the volume of the air gap between the two members. The inclined orientation of one of the pairs of lateral arms (in this case the arms of the rail) to the mutually parallel arms of the other pair results in an increasing attractive magnetic force between the cores 6 and the rail 1 with increasing separation (i.e., with increasing withdrawal of the interfitting parts) to a maximum attractive force at the point that overlap ceases or the poles formed by the ends of the arms become substantially coplanar. At this point, the suspension or guide system becomes unstable as in conventional magnetic suspensions in which the electromagnet cooperates with a flat-strip armature.

If the centers of gravity of the armature rail and the electromagnetic core in any sectional plane perpendicular to the direction of movement of the vehicle and to the longitudinal dimensions of these magnetic members,i.e., the centroids of the sections, are considered to define a longitudinal axis 13 (FIG. 1), it is possible to define the overlapping or interfitting relationship as one which is longitudinally stable without the use of a gap detector or other control arrangement to compensate for increasing separation along this axis.

In other words, a longitudinally stable system, within the meaning of the present inventi0n,is one which compensates automatically for a tendency toward separation of the parts by increasing the magnetic attractive force resisting such separation without a concommitant increase in the electrical energization of the coil. The system of FIG. 1 thus provides increasing magnetic attractive force to resist separation in the direction of the axis 13 until the point of withdrawal is reached.

In the system of FIG. 1, however, a transverse stability (against this location forces in the direction of arrows 10) is not present, i.e., any shift of the system to the left or to the right from the median position shown will not be magnetically resisted by the field 9, but rather will be enhanced so that the system must be laterally stabilized by some external or other means as represented by the forces at 10.

In the system of FIG. 2, the mutually parallel lateral arms, flanks or shanks 12 of the electromagnetic core 6 reach into the channel formed by the armature rail 1 between the inwardly turned arms 2 of the latter. The arms 2 include angles a of less than 90 such that the arms will include the desired angle between 15 and with the arms 12. The overlapping or interfitting relationship which is thus obtained ensures longitudinal stability as described earlier.

FIGS. 3 and 4 represent systems which are kinematic reversal of the systems of FIGS. l and 2. In FIGS. 3 and 4 the arms of the core 6 are inclined inwardly (FIG. 3) or outwardly (FIG. 4) toward the mutually parallel arms 2 of the armature rail 1. The arms of the latter are thus received with an overlap between the arms of the electromagnetic core 6 (FIG. 3) or receive the arms of the core (FIG. 4). The latter systems, which function as described for the system of FIG. 1, have the advantage that a single armature rail structure can be used for a variety of configurations of the magnet or magnet core.

If one desires to modify the force characteristic of the system i.e., the magnetic force versus displacement in the direction of the axis 13, the inclined shanks or arms may be oriented to provide the desired characteristic. For example, in FIG. there is shown a system in which the arms 2 are provided with an outwardly concave curvature i.e., a curvature which is convex in the direction of the centroids. This curvature which may be generally cylindrical, pyramidal or otherwise conformed to a surface of revolution with an axis parallel to the longitudinal direction, results in an increase in the spring constant of the system with increasing longitudinal displacement, i.e., the elastic suspension of the floating system becomes stiffer with greater loads. When the inverse effect is desired, the system of FIG. raise employedin which the arm s are concaved toward the centroid of the armature rail. The term spring constant is used herein to refer'to the relationship between restoring force and displacementwhich, generally speaking, can be represented by a relationship such as F Kx where x is the displacement and F is the restoring force. The constant K is thus defined as F /x and is analogous to the usual spring constant. With increasing K, the system becomes stiffer.

In FIGS. 7 and 8, there are shown two arrangements of the longitudinally stable suspension and guide arrangements of FIGS. 1 through 6. These systems respectively provide a longitudinally stable suspension with an unstable system providing lateral control and an unstable suspension system with a longitudinally stable guide system for lateral control.

The system of FIG. 7, for example,comprises a support track 14 along which a vehicle 15 is displaceable. Along the undersides of the inwardly turned flanges of the track, there are provided a pair of longitudinally stable electromagnetic suspension systems 16 (see FIG. 1) while the guide systems are longitudinally unstable and are provided at 17. The unstable systems 17 each comprises an armature rail 18 and electromagnets 19 with U-profiles whose arms are parallel and aligned one another so that they are juxtaposed without overlap. The electromagnets 20 of these systems are provided with gap detector in their respective control circuits 100 to maintain the optimum gap. However, vertical control circuits are not necessary because of the automatic adjustment of the magnetic adhesion force to increasing displacement in the vertical direction.

A converse system is shown in FIG. 8 in which the longitudinally stable system 21 is provided for guide purposes in combination with longitudinally unstable suspension systems 22, the latter being connected with a control 200 to maintain with optimum suspension gap. The guide systems automatically operate to center the vehicle against lateral forces, e.g., from wind or the centrifugal effect of a turn or bend in the track without a control circuit.

We claim:

1. An electromagnetic suspension or guide system, comprising support, a U-profile armature rail member fixed to said support and having a web and a pair of shanks extending from said web, and electromagnet 5 juxtaposed with said rail member and having a core member provided with a web and a pair of shanks extending therefrom toward said rail member, and a coil wound on said core member, the shanks of one of said members being received between the shanks of the other of said members and overlapping therewith, and at least one shank of each overlapping pair being inclined to the other.

2. The system defined in claim 1 wherein the shanks of said core member extend into said rail member between the shanks thereof.

3. The system defined in claim 1 wherein the shanks of said rail member are received between the shanks of said core member.

4. The system defined in claim 1 wherein the inclined shank of each of said pairs is of curved configuration.

5. The system defined in claim 1 for a magnetically suspended vehicle wherein said support is a longitudinally extending track, said rail member extends longitudinally along said track, said system further comprises a vehicle carrying said electromagnet and displaceable along said track, said core member and said rail member having centroids defining a longitudinal axis of stability such that relative displacement of said vehicle and said support tending to separate said core member from said rail member in the direction of said axis results in a magnetic attractive force counteracting such separation, and a further electromagnetic system effective between said support and said vehicle for stabilizing same against relative displacement in a direction transverse to said longitudinal axis.

6. The system defined in claim 5 wherein said rail member and said core member form a longitudinally stable suspension arrangement for said vehicle, said further electromagnetic system including a control arrangement for limiting lateral displacement of said vehicle and being electromagnetically unstable in the absence of said control arrangement.

7. The system defined in claim 5 wherein said rail member and said core member provide a longitudinally stable lateral guide arrangement for said vehicle and said further electromagnetic system is an unstable electromagnetic suspension including a control arrangement for adjusting the suspension gap of said vehicle.

8. The system defined in claim 5 wherein said armature rail member is provided with a pair of inclined shanks having free ends approaching the shanks of said core member and the shanks of said core member are mutually parallel.

9. The system defined in claim 5 wherein said core member is provided with the inclined shanks having free ends approaching the shanks of said rail member and said rail member has mutually parallel shanks.

10. The system defined in claim 5 wherein the inclined shank of each pair includes an angle between substantially 15 and with the other shank of the pair.

UNITED STATES PATENT AND TRADEMARK OFFICE @ETIFICATE OF CORRECTION PATENT NO. 3,780,668 DATED 25 December 1973 lN\/ ENTOR(S) 1 Peter scEwARzLER and Gerhard BOHN It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, line Q for "Sept. 7, 1971" read Sept.15, 1971 l'gncd and Sealed this [35AM first Day Of June 1976 A rres t:

RUTH C. MASON Commissioner nj'latems and Trademarks 

1. An electromagnetic suspension or guide system, comprising support, a U-profile armature rail member fixed to said support and having a web and a pair of shanks extending from said web, and electromagnet juxtaposed with said rail member and having a core member provided with a web and a pair of shanks extending therefrom toward said rail member, and a coil wound on said core member, the shanks of one of said members being received between the shanks of the other of said members and overlapping therewith, and at least one shank of each overlapping pair being inclined to the other.
 2. The system defined in claim 1 wherein the shanks of said core member extend into said rail member between the shanks thereof.
 3. The system defined in claim 1 wherein the shanks of said rail member are received between the shanks of said core member.
 4. The system defined in claim 1 wherein the inclined shank of each of said pairs is of curved configuration.
 5. The system defined in claim 1 for a magnetically suspended vehicle wherein said support is a longitudinally extending track, said rail member extends longitudinally along said track, said system further comprises a vehicle carrying said electromagnet and displaceable along said track, said core member and said rail member having centroids defining a longitudinal axis of stability such that relative displacement of said vehicle and said support tending to separate said core member from said rail member in the direction of said axis results in a magnetic attractive force counteracting such separation, and a further electromagnetic system effective between said support and said vehicle for stabilizing same against relative displacement in a direction transverse to said longitudinal axis.
 6. The system defined in claim 5 wherein said rail member and said core member form a longitudinally stable suspension arrangement for said vehicle, said further electromagnetic system including a control arrangement for limiting lateral displacement of said vehicle and being electromagnetically unstable in the absence of said control arrangement.
 7. The system defined in claim 5 wherein said rail member and said core member provide a longitudinally stable lateral guide arrangement for said vehicle and said further electromagnetic system is an unstable electromagnetic suspension including a control arrangement for adjusting the suspension gap of said vehicle.
 8. The system defined in claim 5 wherein said armature rail member is provided with a pair of inclined shanks having free ends approaching the shanks of said core member and the shanks of said core member are mutually parallel.
 9. The system defined in claim 5 wherein said core member is provided with the inclined shanks having free ends approaching the shanks of said rail member and said rail member has mutually parallel shanks.
 10. The sYstem defined in claim 5 wherein the inclined shank of each pair includes an angle between substantially 15* and 60* with the other shank of the pair. 